docs: def get_star(self, node):
          """Given a node, get a copy of that node's star, that is, the set of
          hyperedges that the node belongs to.
  
          :param node: node to retrieve the star of.
          :returns: set -- set of hyperedge_ids for the hyperedges
                          in the node's star.
          :raises: ValueError -- No such node exists.
  
          """
          if node not in self._node_attributes:
              raise ValueError("No such node exists.")
          return self._star[node].copy()